1. Field of the Invention
This invention relates generally to telecommunications systems, and, more particularly, to wireless telecommunications systems.
2. Description of the Related Art
Wireless telecommunications systems may be used to connect mobile units (sometimes also referred to as user equipment or UE) to a network using an air interface. Mobile units may include mobile phones, personal data assistants, smart phones, text messaging devices, laptop computers, desktop computers, and the like. For example, a mobile phone may be used to form a communication link over an air interface that operates according to a Code Division Multiple Access (CDMA2000) Evolution—Data-Optimized (EV-DO) standard or a Universal Mobile Telecommunication Systems (UMTS) standard. For another example, a wireless-enabled laptop computer may connect to the Internet by forming a communication link with an access point over an air interface that operates according to an IEEE 802.11 standard. Many mobile units are capable of communicating with more than one type wireless telecommunications system. For example, a dual-radio smart phone may include network interfaces for an EV-DO network and an IEEE 802.11 network.
Despite the proliferation of wireless technologies, no single technology meets all the potential requirements of applications in the mobile units while also providing sufficient user mobility. Instead, different wireless technologies typically attempt to balance competing demands, e.g. for network capacity and a large coverage area. For example, wireless local area network (LAN) technology provides relatively high capacity over a relatively small range, but the range of access points in the wireless LAN may be too short to cover a large geographical area with reasonable infrastructure cost. In contrast, wide-area wireless technology, such as EV-DO or UMTS networks, may provide coverage to a relatively large area but may limit a per-user bandwidth to values that are typically much smaller than that of wireless LANs.
Overlay networks attempt to combine advantages of different wireless technologies in a single architecture. In the overlay network architecture, multiple layers of cells (each potentially using a different technology) form a hierarchical cell structure. For example, a simple two-layer wireless overlay network may be formed by using the IEEE 802.11 wireless LAN technology for relatively high-bandwidth/small-size cells at the bottom layer and a Third Generation (3G) cellular wireless technology for relatively low-bandwidth/large-size cells at the top layer. Exemplary 3G cellular wireless technologies may include, but are not limited to, EV-DO networks, UMTS networks, and High Speed Downlink Packet Access (HSDPA) networks.
Wireless overlay network architectures are becoming increasingly important and widespread. Hotspot cells, such as IEEE 802.11 cells, are being deployed in places like airports, hotels, shopping malls, coffee shops, and the like. Umbrella coverage may then be provided via one or more 3G wide area cellular base stations, such as for example EV-DO or UMTS base stations. Typically, base stations and IEEE 802.11 hotspot access points use wireline connections such as a T1 or Ethernet for a backhaul link to the wired network. Hotspot services may also be provided in transportation systems such as commuter trains, buses, ferries, airplanes, and the like. Hotspots in transportation systems may be mobile and therefore the access points in the mobile hotspots may require wireless backhaul links. For example, the overlay network may include a wireless backhaul link between access points of the mobile hotspot cells and a base station (or node-B) of a 3G cellular network.
A single radio mobile unit may connect to the access point in the hotspot cell, which may then function as a gateway or relay to a base station in the 3G umbrella network. Thus, the access point may enable wide-area coverage for the single-radio mobile units that only have wireless LAN technology A dual-radio mobile unit may form wireless links with an access point in the hotspot or with a base station in the 3G umbrella network. In some instances, dual-radio users may prefer to connect to the access point in the hotspot cell, which may then function as a gateway or relay to a base station in the 3G umbrella network. Such an indirect transmission path may be advantageous since the connection to the base station may not be as good as the connection to the gateway access point. In addition, the presence of the gateway access point may simplify call management in the 3G network. Indeed, if many mobile units attempt to link directly to the 3G base station, the 3G base station may not be able to efficiently set up and handle the call processing involved for all the mobile units. Deploying a gateway access point may offload some of that processing to the gateway access point, which looks like a single mobile unit to the 3G base station, thereby reducing the processing burden on the 3G base station.
A hotspot cell with a wireless backhaul connection can also serve as an aggregation point for multiple mobile units with dual-radios. Thus, the gateway access point may be able to achieve some statistical multiplexing gains by aggregating the mobile units, which may facilitate buffer management in the network. For example, the variability of the individual traffic streams may be significantly reduced, which facilitates the network management and leads to increased performance. For another example, packing efficiencies may be achieved at the Transmission Control Protocol (TCP) layer, which may allow the gateway access point to maintain a persistent TCP connection to the base station and avoid setting up, tearing down, and re-establishing connections for the different mobile units. The smoother aggregate stream of packets may not be exposed to the variability of the individual packet streams. Therefore some of the adverse effects in TCP, such as TCP slow start and timeouts, can effectively be avoided, leading to a larger aggregate system throughput.
However, as discussed above, the umbrella network typically treats the gateway access point as a single user. For example, a 3G EV-DO base station is generally not aware that one or more of the 3G “users” may not be a physical user but rather an IEEE 802.11 hotspot access point and/or a mobile gateway that serves as a relay to multiple physical users through the IEEE 802.11 air interface. In that case, the 3G EV-DO base station may treat the IEEE 802.11 access point as a single user, even though the IEEE 802.11 access point may be providing wireless connectivity to several physical users. Consequently, the scheduling algorithms employed by the umbrella network may not distribute capacity in the expected and/or desired manner to the “physical” end-users, some of which are one hop away from the EV-DO base station and some of which are more than one hope away from the EV-DO base station.
One goal of conventional scheduling algorithms is to achieve the largest possible utilization of limited air interface resources. Conventional 3G wireless networks employ opportunistic scheduling algorithms, such as the well-known Proportional Fair (PF) scheduling algorithm that is implemented in many EV-DO products. Opportunistic scheduling algorithms take advantage of the time-varying nature of a wireless channel to schedule users when their relative channel conditions are favorable, while at the same time providing a certain degree of fairness to all the competing users. When the “users” include both physical users that are directly connected to a 3G base station and wireless backhaul links from mobile gateways, the scheduling algorithm employed at the EV-DO base station may fairly distribute the network capacity between the users directly connected to the base station and the mobile gateways. However, end-user devices coupled to the mobile gateway are not visible to the scheduling algorithm and consequently may not receive the expected and/or desired quality-of service or fairness.
As an illustrative example, consider an EV-DO scheduler that attempts to give equal throughput to three mobile units directly connected to an EV-DO base station and three other mobile units connected to the EV-DO base station through a single mobile gateway. The EV-DO scheduler attempts to provide equal throughput to all the mobile units, i.e. the EV-DO scheduler attempts to provide each mobile unit with approximately ⅙ of the total throughput available to the EV-DO base station. However, the EV-DO scheduler only sees four EV-DO “users” (three mobile units and the mobile gateway) and therefore attempts to provide each “user” with approximately ¼ of the total throughput of the EV-DO base station. If a scheduler at the mobile gateway is also fair and divides its available throughput equally between users, then the three mobile units connected to the mobile gateway will receive approximately ⅓ of the throughput available to the mobile gateway, or approximately 1/12 of the throughput of the EV-DO base station. In contrast, the three physical users in the wide-area network receive approximately ¼ of the total throughput of the EV-DO base station. Thus, the EV-DO scheduler may not be able to provide equal throughput to all the mobile units.
The present invention is directed to addressing the effects of one or more of the problems set forth above.